x d drilling fluid



, Reissued Dec. 21, 1943 ,UNITED STATE Re. 22,407 I s PATENT f OFFICE I r DRILLING FLUID Frederick Konrad Daniel, Kew Gardens, N. 2., as-

signor to Hornkem Corporation, Long Island City, N. Y., a corporation of New York No Drawing. Original No. 2,328,426, dated August 228,888, August 26, 1938. Application for reissue 31, 1943, Serial No.

6 Claims.

a mud sheath on the wall of the hole and there-- by retard caving and sloughing; to seal ofl minor gas, oil and water bearing formations; by its hydrostatic head to suppress formation pressures;

to lubricate the bit and drill pipe; and to cool the bit.

In providing a drilling fluid which will accomplish all of these functions, the fluid has to be of carefully balanced consistency and its viscosity" should be as low as possible, or rather its mobility should be as high as possible while the fluid is in motion and the drill is operating.

n the other hand, it is also desirable that the liquid should form a gel upon standing. and that such a gel should have a low yield value and should break down to a liquid when the drilling operation is resumed. While the drilling fluid should set to a gel relatively slowly it should be instantaneously and easily broken up to form again the original low resistance drilling fluid when the drilling has been resumed.

In most cases, the native drilling fluids do not contain suflicient colloidal material to give themud the desirable properties.

Bentonitic clays are therefore generally used to make the drilling fluid thixotropicias the described isothermal sol-gel transformation is called. However, in most cases the addition of these bentonitic clays causes the viscosity to be high. the time of solidification of this thixotropic drilling fluid to be too short and the gel strength to be too high.

I Particularly where this drilling fluid has a high solid content, and/or an excess of free polyvalent cation and/ or a wrong pH range, the time of'solidiflcation, i. e., the time required to convert the drilling fluid or liquid into a gel state, becomes very short and may be onlya fraction of a second. Such liquids substantially behave like gels at all times and they do not function most satisfactorily as drilling fluids. In addition, the viscosity and gel yield value with such drilling fluids is greatly increased.- whereas with the most October 7, 1943, Qerlal as c1ays,'barytes, etc.

satisfactory drilling liquid all that is desired is a low viscosity and low yield value, just sufllcient to prevent rapid settling of the cuttings or the drilling residue in the hole when the drilling operation is suspended and to prevent the settling of the suspended particles forming part of the mud, such As an example of the which it is desired to attain, the following characteristics may be given:

Viscosity 15 centipoise for a 10 /2 lb. mud. Initial gel in Stormer viscosimeter, 10 grams. Gel after 10 minutes, -grams.

The pH of the fluid should lie between approximately 8 and 9.5.

It is the primary object of this invention to bring a colloidal drilling fluid into a condition as close as possible to the one characterized above.

It is also the object of the present invention to provide an improved drilling fluid which will be relatively stable during drilling operations, even though sucha drilling fluid may be or become contaminated with acidic or alkaline materials tending to derange its pH value or become contaminated with fluids or liquids containingva- I rious salts and particularly calcium or magnesium I salts which may tend tocause flocculation and/or thickening of the fluid.

A further object of the present invention is to pIOVlOe an improved drilling fluid oi the character above described in which there will be no tendency toward burning" the fluid, i. e., separation of a solid phase in the gel from water (syneresis) and in which the drilling fluid will maintain a high degree of balance at all times.

Other objects will be obvious or will appear in the more detailed description set forth below. a

In accomplishing the above objects, it has been found most satisfactory to increase the mobility and time of solidification of the fluid and to decrease the yield value of the gel by including in the drilling fluid certain types of phosphates, preferably those with at least two phosphorous atoms per molecule, which are stable at a pH of pyrophosphates (All: MeiPro'n or theacid pyrophosphates (Alk MeuHzPzOw) may be utilized by themselves. it is generally found most satisfactory to utilize a combination of tetrasodium or-tetratype of drilling mudmagnesium salts.

potassium pyrophosphate, havin an alkaline reaction, and the corresponding acid. pyrophosphates having an acid reaction.

, The proportions of acid and normal pyrophosphate may be .varied, but preferably they should be in a proportion where the resulting pH lies be-' tween 8 and 9.5. f

This pyrophosphate solution will be highly stable and will difl'er in this respect from a metaphosphate-containing mud or drilling fluid. For example, with a drillingfluid having the optimum pH range from 8 to 9.5, sodium or potassium metaphosphate will tend todecompose into an orthophosphate, particularly at the relatively: elevated temperatures usually occurring in oil wells.

As a result, in order to maintain a proper drilling mud, it would be necessary to continue to add the metaphosphate and as the metaphosphate is added and is converted into the orthophosphate there will result an increase in acidity and a decrease of the pH value of the whole system. In 1 turn this will cause thickening of the drilling fluid, and will counteract to a certain extent the initial thinning eflect of the metaphosphate.

The pyrophosphate mixture having a pH range of 8 to 9.5 produces a most homogeneous and stable drilling fluid with a high degree of balance which will be highly mobile, and which will only solidify to a gel of low yield valueafter a relatively long time, which gel may be readily broken up to a fluid when the drilling operation is initiated or resumed.

,In drilling fluids or muds, difficulties often arise whenusin'g phosphates, including pyrophosphates' and metaphosphates, because of the tendency of these compounds to react with calcium, magnesium and other polyvalent cations always present in such fluids or muds.- These reactionproducts do not have the desirable mud-enhancing properties of the above mentioned phosphates.

In counteracting this tendency and in restoring the balance of the drilling fluid, if it has already become contaminated as for example by salt water, it has been foundmost suitable to add various types of soluble precipitants for the calcium and magnesium salts whichwill have a great tendency to react with the calcium and These precipitants thus will remove such salts from .the drilling fluid or convert them into insoluble form before they have had a chance to react with or precipitate the metaphosphates or the pyrophosphates. Among the most satisfactory precipitants or balancing salts of this character, is trisodium or tripotasslum orthophosphate and sodium or ammonium or potassium oxalate. Generally such trisodium phosphate, where employed, may be utilized in an amount varying, say from 2 to parts forevery 100 parts of the pyrophosphate ,When abnormal conditions of saltwater or other contaminations are found, according to this invention an extra quantity of such precipitants may be. added together with the pyrophosphates or metaphosphates, but-preferably before the pyrophosphates are added, the object being to preserve the. full strength and activity of the pyrophosphates orv other mud-treating chemicals.

change so that it will be without the preferred range of 8 to 9.5.

This contamination may be caused by an inclusion of various alkaline or acid waters or liquors in the drilling fluids from various strata, or

/ by inclusion of improper mud treating chemicals In addition to the possibility of contamination 7 with precipitating salts, such as calcium or magor other conditions tending to cause its pH to or even by inclusion of metaphosphate which might tend to give rise to the production of an acid when it is converted into an orthophosphate under the temperature and pH condition existing within the mud.

Although many combinations may be employed to buffer or protect the drilling fluid or mud from the change of pH, it has been found that the mostsatisfactory materials are combinations of relatively weak acids and their salts, such as for example combinations of boric acid and its salts or combinations of orthophosphoric acid salts.

In the former case it is possible to utilize a combination of boric acid and borax or some other sodium borate and in the latter case it is possible to utilize a combination of trisodium phosphate with either one or both of the corresponding acid phosphates, such as disodium hydrogen orthophosphate or dihydrogen sodium orthophosphate.

The ratio of borax to boric acid or of any other bufier components should be such as to maintain a DH of 8 to 9.5.

These buffer mixtures are generally utilized in amounts varying from /i to 5 parts for every 10 parts of the pyrophosphate. These buffer combinations are particularly useful in drilling fluids which may be devoid of pyrophosphates or metaphosphates or other mud treating agents, in erihancing such drilling fluids or correcting such drilling fluids if they are not in properbalanced condition.

In such cases where the pH is far removed from the preferred range such quantities of the buffer alone or in combination with phosphates or other mud treating chemicals may be used as to bring mud back to its proper pH.

It has been found that the borax-boric acid bufier and the orthophosphate buffer often bring down the viscosity and gel strength of the mud so that the amount of pyrophosphate may be decreased or so that the pyrophosphate may be omitted. 3

An example of one type of a, composition for treatingdrilling fluids is the following:

Pounds Tetrasodium pyrophosphate (anhydr0us) 34.35 Acid pyrophosphate 18.90 Borax 15.45 Boric acid 13.75 Trisodium phosphateuu; 3.45

phate is wanted, the sodium pyrophosphate may be partly or wholly replaced by tetrapotassium pyrophosphate. The latter is soluble to a very high degree, whereas only 6.5 parts of anhydrous tetrasodium pyrophosphate may be dissolved in parts of cold water. K4P2O7 is slightly more alkaline than Na4PzO1, so that a little more acid pyrophosphate should be used in conjunction with the former in order to get the desirable pH range. Tetrapotassium pyrophosphate is a little less effective in reducing properties than the tetrasodium pyrophosphate.

The following is an example of a bufier solution having the desired pH which may be added alone to a drilling mud or in addition' to the above combinations or together with the calcium precipitating compound:

This may be. readily dissolved in 600 lbs. of water.

Of course, where the trisod'ium phosphate is used as part of the butter mixture, suillcient of it may also be included to, react with the/calcium and magnesium salt to remove them from the drilling fluid before action with the pyrophos-, phates present. In addition to these bufi'er combinations above stated, any other bufier combination producing a pH range of between 8 and 9.5 may be employed.

The combinations of the mud treating chemicals above described will give to drilling fluids a high stability and balance and will cause them to In addition to the alkaline metal sa ts of pyrophosphates; it is also possible to use various phosphates of higher molecular weight than the resist any change in pyrophosphate efficiency or pH value upon contamination with alkaline or acid liquors or water containing dissolved cal-.

cium or magnesium salts. I

The treated drilling fluids will have a prolonged solidification time so that a gel will not form momentarily therein when the drilling has been stopped and at the same time the gel will have a low yield value so that it may be readily reconverted into a liquid upon resumption of the drill-' ing operation.

Moreover, the fluid will most satisfactorily cool the pipe and bit and also most satisfactorily lubricate the bit during the drilling operation. It will have such consistency as to prevent quick settling of suspended rock particles and other large suspended particles in the well and yet it will not allow gas to become entrained in the mud,

or if it does, it will permit it readily to escape.

At the same time the drill fluid will maintain the suspension of the flnely divided clay, iron oxides or barytes particles which are substantially finer than 200 mesh, while the larger suspended particles can be removed comparatively easily.

Furthermore, in many cases the boric acidborax combination in itself acts to enhance the stability and balance of the drilling fluid and in certain conditions a boric acid-borax combination may be utilized to lower viscosity and in crease the time of solidification in addition to having a buffer effect.

pyrophosphates and also combinations of phosphates with metallic oxides such as combinations with vanadium oxide, iron oxide and other metal oxides. v i g Isl;

. It is to be understood that the various specific proportions and compounds above mentioned have been mentioned by way of illustration and not by way of limitation and that many alternatives, modiflcations and changes may be made in the above identified procedures and compositions specifically described without departing from the essential features of the present invention, all of which it is intended to cover broadly by the present invention.

What is claimed is:

1. A method of treating a colloidal drilling fluid which comprises adding thereto a mixture of alkali metal acid and normal pyrophosphates having a pH between 8.0 and 9.5.

2. A process of correcting and protecting drilling muds which comprises adding thereto a combination of alkali metal normal and acid pyrophosphates and a buffer reagent capable of maintaining a pI-I of between 8 and 9.5. I

3. A method of treating a colloidal drilling fluid which comprises adding thereto a composition of pH between 8.0 and 9.5 and substantially consisting of tetrasodium pyrophosphate (NaiPto'l), an acid pyrophosphate-(NaaHzPzO-zl borax and boric acid.

4. A method of treating a colloidal drilling fluid which comprises adding thereto a mixture of tetra-alkali metal pyrophosphate and an acid alkali metal pyrophosphate containing a buffer substantially consisting of borax and boric acid said mixture having a. pH between 8.0 and 9.5.

5. A stabilizing mixture for addition to a thixotropic mud drilling fluid which consists substantially of tetrasodium pyrophosphate, disodium acid pyrophosphate, borax, boric acid and trisodium orthophosphate in aqueous solution having ,a pH between 8.0 and 9.5,.

6. A stabilizing mixture for addition to thixotropic mud drilling fluid which consists substantially of dissolved in-BOO to 500 parts by weight of water, said mixture having a pH between 8.0 and 9.5. FREDERICK KONRAD DANIEL. 

